Re: [PATCH] vasnprintf: Don't use %n on android

[Tim Rühsen]

On 1/21/19 5:00 PM, Hugo Beauzée-Luyssen wrote:
> On Mon, Jan 21, 2019, at 4:58 PM, Tim Rühsen wrote:
>> On 1/8/19 2:22 PM, Hugo Beauzée-Luyssen wrote:
>>> On Thu, Dec 20, 2018, at 2:53 AM, Bruno Haible wrote:
>>>> Hi,
>>>>
>>>> Hugo Beauzée-Luyssen wrote:
>>>>> 12-14 19:10:02.633 F DEBUG   : pid: 31664, tid: 32389, name: VlcObject  
>>>>> >>> org.videolan.vlc <<<
>>>>> 12-14 19:10:02.633 F DEBUG   : signal 6 (SIGABRT), code -1 (SI_QUEUE), 
>>>>> fault addr --------
>>>>> 12-14 19:10:02.633 F DEBUG   : Abort message: 'FORTIFY: %n not allowed on 
>>>>> Android'
>>>>
>>>> Indeed, %n in *printf is not allowed on Android, see
>>>> https://android.googlesource.com/platform/bionic/+/master/libc/stdio/vfprintf.cpp
>>>> https://android.googlesource.com/platform/bionic/+/master/docs/status.md
>>>>
>>>>> diff --git a/lib/vasnprintf.c b/lib/vasnprintf.c
>>>>> index af3fcd1c7..e41d5f706 100644
>>>>> --- a/lib/vasnprintf.c
>>>>> +++ b/lib/vasnprintf.c
>>>>> @@ -4874,7 +4874,8 @@ VASNPRINTF (DCHAR_T *resultbuf, size_t *lengthp,
>>>>>  # if ! (((__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3))     
>>>>>    \
>>>>>           && !defined __UCLIBC__)                                         
>>>>>    \
>>>>>          || (defined __APPLE__ && defined __MACH__)                       
>>>>>    \
>>>>> -        || (defined _WIN32 && ! defined __CYGWIN__))
>>>>> +        || (defined _WIN32 && ! defined __CYGWIN__)                      
>>>>>    \
>>>>> +        || defined __ANDROID__)
>>>>>                  fbp[1] = '%';
>>>>>                  fbp[2] = 'n';
>>>>>                  fbp[3] = '\0';
>>>>
>>>> The patch looks good at first sight. But when you look at the comments a
>>>> couple of lines before it, you see that one can avoid %n only
>>>> if snprintf behaves well enough. To this effect, can you please report
>>>> the configure results (from a *native* Android compilation, not a cross-
>>>> compilation) of these tests:
>>>>
>>>> 1 = checking whether printf supports size specifiers as in C99...
>>>> 2 = checking whether printf supports 'long double' arguments...
>>>> 3 = checking whether printf supports infinite 'double' arguments...
>>>> 4 = checking whether printf supports infinite 'long double' arguments...
>>>> 5 = checking whether printf supports the 'a' and 'A' directives...
>>>> 6 = checking whether printf supports the 'F' directive...
>>>> 7 = checking whether printf supports the 'n' directive...
>>>> 8 = checking whether printf supports the 'ls' directive...
>>>> 9 = checking whether printf supports POSIX/XSI format strings with 
>>>> positions...
>>>> 10 = checking whether printf supports the grouping flag...
>>>> 11 = checking whether printf supports the left-adjust flag correctly...
>>>> 12 = checking whether printf supports the zero flag correctly...
>>>> 13 = checking whether printf supports large precisions...
>>>> 14 = checking whether printf survives out-of-memory conditions...
>>>> 15 = checking for snprintf...
>>>> 16 = checking whether snprintf truncates the result as in C99...
>>>> 17 = checking whether snprintf returns a byte count as in C99...
>>>> 18 = checking whether snprintf fully supports the 'n' directive...
>>>> 19 = checking whether snprintf respects a size of 1...
>>>> 20 = checking whether vsnprintf respects a zero size as in C99...
>>>>
>>>> You should find these in the configure output of any package that
>>>> uses gnulib's 'vasnprintf' module. If you don't have one at hand,
>>>> create one using
>>>>   ./gnulib-tool --create-testdir --dir=testdir --single-configure 
>>>> vasnprintf
>>>>
>>>> Thanks.
>>>>
>>>> Bruno
>>>>
>>>
>>> Hi,
>>>
>>> I'm probably missing something, but for me this only seems to test for 
>>> snprintf/printf/vasnprintf availability (including running configure in the 
>>> generated test directory)
>>
>> I would really like to see the patch in gnulib as soon as possible.
>>
>> @hugo If it's not too much hassle, could you please provide the
>> requested information ?
>>
>> Regards, Tim
>>
> 
> Hi,
> 
> I'd love to, but I failed to fetch those so far. The provided command line 
> didn't return any valuable information, and simply tested for the presence of 
> various printf family function.
> 
> Regards,

So you cd'ed into testdir and run `./configure` !?

I also don't see much here (Debian unstable):

$ grep -A1 -i 'checking.*printf' config.log
configure:6305: checking for vasnprintf
configure:6305: result: no
configure:6305: checking for snprintf
configure:6305: result: yes
--
configure:8450: checking whether snprintf returns a byte count as in C99
configure:8548: result: yes
configure:8559: checking for snprintf
configure:8559: result: yes
--
configure:8568: checking whether _snprintf is declared
configure:8568: result: no

What does that grep look for you ?

@Bruno Is there something missing ?

Regards, Tim

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